1. Field of the Invention
The present invention relates to a fresh gas system for a piston engine, in particular in a motor vehicle. The invention also relates to an operating method for a piston engine equipped with such a fresh gas system.
2. The Prior Art
EP 0 547 566 B1 discloses a fresh gas system for a piston engine equipped with a collecting line for supplying fresh gas to several individual lines. Each individual line supplies fresh gas to one combustion chamber of the piston engine, with an intake valve being provided for each cylinder of the piston engine for opening and closing a connection between the respective combustion chamber and the respective individual line. In addition, upstream from the intake valve, an additional valve with which the respective individual line can be opened and closed is provided in each individual line.
With the known fresh gas system, the fresh gas supply to the combustion chambers can be influenced with the help of the additional valves so that an increase in temperature beyond the adiabatic final compression temperature is established in the respective cylinder. This operating behavior of the piston engine may also be referred to as heat charging.
DE 43 08 931 C2 discloses an operating method for a piston engine which is known as pulsed supercharging. In this method, the respective intake valve in the respective combustion chamber is closed briefly during an intake stroke of the respective piston. The resulting dynamic flow effects lead to the desired pulsed supercharging of the respective combustion chamber.
In addition, it is also known from Pischinger “Variable Valve Control II,” Expertverlag [Expert Publishers], pages 244 to 260, that the fresh gas system in a piston engine can be unthrottled upstream from intake valves, whereby to implement the fresh gas charging, which depends on the respective load state of the piston engine, the opening and closing times of the intake valves are adapted accordingly. It is known in particular that two intake time windows may be implemented for the respective intake valve during an intake stroke of the respective piston, the first of which is at the beginning of the intake stroke while the second intake time window is at the end of the intake stroke. The unthrottled or throttle-free fresh gas system is characterized by the absence of a throttle valve, which is situated in the collecting line in a traditional fresh gas system to throttle the fresh gas supply of the combustion chambers as a function of the current load state of the piston engine in partial-load operation of the piston engine. The throttled fresh gas supply is problematical because considerable charge cycle losses occur and the reduced velocities of flow associated therewith hinder the formation of a mixture. The quality of the combustion process then suffers, leading to comparatively poor emission values and increased fuel consumption values. In the case of throttle-free or unthrottled fresh gas supply, the quality of the combustion process can be improved significantly, which results in reduced emissions and fuel consumption values.
To be able to implement the desired control of the fresh gas charge, i.e., control of the volume of fresh gas when the fresh gas system is unthrottled, the known piston engine operates with an electromagnetic valve control unit, which makes it possible to arbitrarily open and close the intake valves. However, such electromagnetic valve control units are much more expensive than traditional valve drives controlled by camshafts.